The invention concerns a method of producing fibre-reinforced concrete in which a lattice-like mesh of threads is made, and it concerns shaped parts manufactured by this method.
The term "shaped parts" here includes construction slabs.
From German Patent Specification No. 41 435 a method of the category mentioned above is known in which strands or rods of glass fibres--preferably prestressed--are embedded in concrete. The purpose of the fibreglass rods here is to take the place of the usual metal reinforcement. By soaking the fibreglass rods with suitable resins they are protected against chemical attack, and at the same time they are made stable with respect to shape. In order to enhance the adhesion between the concrete and the reinforcement rod quartz sand is sprinkled over the soaked rods, or resin-soaked fibreglass strands are wound helically around the rods. In this method, where the fibreglass bars merely take over the function of a steel reinforcement and where the grains of quartz sprinkled onto the fibreglass rods merely produce the bond between the concrete and the fibreglass rod, no multi-directional, elastic reinforcing lattice is produced.
From German Patent Specification No. 39 245 a reinforcing unit for concrete, made from fibreglass-reinforced plastics, is known, where a granular material of quartz flour and fine stone chips is applied to the reinforcing unit, or the unit has profiled strips wound helically around it, in order to enhance the adhesion between the unit and the concrete. Again, no flexible, multi-directional, reinforcing lattice is obtained with the application of reinforcing units treated in this way.
From the documentation of German Design Patent (Gebrauchsmuster) No. 70 18 657, metal reinforceing rods, preferably for plastic parts, are known which possess bends whereby the reinforcing rods are anchored in the plastic.
In other known methods asbestos is used as a reinforcing fibre. In this case cement is used as a hydraulic bonding agent in order to process the relatively fine fibres which are often only a few millimeters in length. The method is reminiscent of the manufacture of cardboards. Fine asbestos-cement fleeces running one over the other are formed on a drum until the desired thickness is reached. They can then be taken off and compacted under pressure.
This method is effective even with the addition of very large amounts of water to the asbestos-cement mix. The bonding power of the cement remains intact owing to the close hydraulic union with the mineral fibres.
However glass or synthetic fibres cannot be processed by this method. The bonding force of the cement is lost.
The use of asbestos fibres leads to a number of annoying disadvantages. Their poor breaking elasticity restricts the applicability of the products, and the asbestos dust produced when the slabs are cut is extremely carcinogenic.
Methods of working alkali-resistant glass fibres into concrete are also known. In these methods glass fibres are first added in the concrete mixer. This leads to mixing problems (hedge-hogging and coagulation) and also injuries to the fibreglass surfaces which greatly impair the durability of the product.
Another method is based on the use of a concrete-spraying nozzle which brings semi-liquid cement mortar together with small quantities of chopped glass fibres. These fibres drop onto a support and while some are already bonded with the cement as they drop, others are only embedded in the paste on the support. This does indeed result in a multidirectional reinforcement, but the method is very labour-intensive and depends on the reliability of the workmanship. For example, if a number of fibre fragments drop on top of each other the bulk cement cannot penetrate the intervening spaces. Weak points in the reinforcement arise which will result in fracture when the finished parts are subjected to loading.